The multilayer wiring structure in a semiconductor device is formed by burying a metal wiring in an interlayer insulating film. A Cu (copper) is used as a material for this metal wiring because of low electromigration and low resistance, and a damascene process is commonly utilized as a forming process.
In this damascene process, a trench for burying a wiring, which is to be arranged inside a layer, on an interlayer insulating film in a substrate, and a via hole for burying a connection wiring, which connects upper and lower wirings, are formed, and a Cu is buried on these depressed portions by a CVD or an electrolytic plating method. And, in order to favorably perform the burying of the Cu, it is necessary to form a very thin Cu seed layer along the inner face of the depressed portion on the surface of the interlayer insulating film in a case when the CVD method is used, and it is also necessary to form a Cu seed layer, which becomes an electrode, on the depressed portion in a case when utilizing the electrolytic plating method is used. Further, because the Cu is easy to diffuse in the insulating film, it is necessary to form, for example, a barrier film, which consists of a laminated body of Ta/TaN, on the depressed portion. Therefore, the barrier film and the Cu seed layer are formed on the surface of the depressed portion by, for example, a sputtering method.
By the way, the miniaturization of a wiring pattern has been progressing. As a result, it is necessary for the barrier film and the seed layer to be a further thin layer. However, in a case when forming the barrier film and the seed layer, the metal forming them is formed in a thick layer around the opening compared to the deep part of the depressed portion because the width of the depressed portion is miniaturized. For this reason, it is difficult to form the barrier film and the seed layer with a high uniformity in the depressed portion, thus the reliability against a barrier property, and the contactability of an interface with the seed layer is an issue.
Based on such background, the Japanese Published Unexamined Patent Application No. 2005-277390 (paragraph 0018 to 0020, FIG. 1 and so on) discloses a method for forming an alloy film of Cu and an additive metal, such as Mn (manganese), along the surface of a depressed portion of an insulating film, and subsequently forming a barrier film by annealing. More specifically, by the annealing, the Mn in the alloy moves so as to discharge from the Cu, so that a portion of Mn diffuses on the surface of the interlayer insulating film and reacts with the O, which is a constituent element of the interlayer insulating film. As a result, a self aligning barrier layer, such as an oxide MnOx (x is a counting number) or MnSixOy (x and y are counting numbers) that is an extremely stable compound, is formed. Along with this, an excess Mn, which was not utilized in the forming of the barrier layer, moves to the surface side of the alloy film (the opposite side of the interlayer insulating film), and the moved Mn is removed at a subsequent process. The self-aligning barrier film formed in this way will be extremely uniform and thin, thereby it contributes in resolving the issue described above.
By the way, in order to form the barrier film described above efficiently, it is preferable to configure the Mn concentration higher as the lower the layer of the alloy film, it enables the reaction of the Mn with the interlayer insulation film easier, and also when the Mn concentration is lower, the greater the layer of the alloy film, which makes it easy to diffuse and deposit the residual Mn on the surface of the alloy film by the concentration gradient of the Mn in the film. By forming the alloy film in a way that the concentration gradient is formed, the residue of the Mn on the seed layer can be suppressed, and as a result, an increase in the wiring resistance can also be suppressed. Further, since the Mn can be diffused in a low temperature, the heat history until the wiring to be formed can also be suppressed thereby the damage to the wiring can be suppressed.
In order to provide the concentration gradient of the Mn as described above, forming the alloy film by a chemical method, such as the CVD (Chemical Vapor Deposition), to change the amount of gas, which contains a deposition component supplied to the depressed portion, with time can be considered. However, because when forming a film by such a method, the control width of the gas is small because an organic liquid source is vaporized, thus a large concentration gradient can not be provided.
Therefore, for example, forming the alloy film with the concentration gradient of the Mn as described above by a physical method, such as sputtering like a PVD (physical vapor deposition), can be considered. However, in such a case, it is necessary to use Cu alloys with different Mn concentrations as a metal target, which requires treatment vessels for the number of that targets for storing the target to process a substrate. As a result, the size of the film forming apparatus increases and the substrate is needed to be transferred between the treatment vessels, which results in a decrease in throughput.
Also, other than the case where forming the self-aligning barrier film as described above, a wiring metal may be formed on a substrate so as to include an additive metal to suppress the electromigration. For example, in a case when forming a wiring with Al (aluminum), film is formed such that a few atomic percent of a Cu is contained in the Al, and the Cu atom enters the gap formed between the Al atoms, thereby preventing the Al moving and the electromigration is suppressed. Further, in a case when forming a wiring with a Cu, an atom, such as Ag (silver), or Sn (tin), as an impurity.
For example, in a case when forming a wiring contains an additive metal to suppress the electromigration in such way after forming the barrier film and the seed layer on the depressed portion as described above, the additive metal being in a high concentration near a position closer to the barrier film in the seed layer is advantageous for increasing the electromigration resistance.
Also, in a case when forming one layer of an alloy film on each substrate by performing the film forming treatment using a sputtering film forming apparatus, it is necessary to change the metal target in a treatment vessel of the apparatus when attempting to change the concentration of the additive metal contained in the alloy film according to the type of the substrate.
For this reason, it is bothersome work to replace the metal target by opening the vacuum container, which is required, and also, the vacuuming after the replacement work takes long time.